[2] From the early 1940s, O'Hanlon was a character actor in feature films, usually playing the hero's streetwise, cynical friend.

He also made various appearances on ABC's Love, American Style, a series for which he wrote the teleplays and also directed several episodes.

In 1971, O'Hanlon appeared as a bear trainer on The Partridge Family, season 2, episode 6, "Whatever Happened to Moby Dick?

[3] In the mid-1980s, Hanna-Barbera revived The Jetsons and brought back its original voice cast of O'Hanlon, Daws Butler, Mel Blanc, Don Messick, Penny Singleton, Jean Vander Pyl, and Janet Waldo.

[6][7] On February 11, 1989, just after he finished recording his dialogue for Jetsons: The Movie,[3] O'Hanlon complained of a headache and was taken to Saint Joseph's Hospital in Burbank, California, where he died of a second stroke.

[8] According to Andrea Romano, who was Hanna-Barbera's casting director at the time, O'Hanlon found it difficult to read and hear, and in the end, he died doing what he loved.